Multiple Sclerosis (MS) is a chronic autoimmune disease where the immune system attacks the protective myelin sheath surrounding nerve fibers in the central nervous system. This damage disrupts communication between the brain and the body, leading to a wide range of neurological symptoms. Dry eye syndrome (keratoconjunctivitis sicca) occurs when the eye does not produce enough tears or produces poor-quality tears, causing discomfort, irritation, and visual disturbances. The connection between MS and chronic dry eye symptoms is a recognized association that impacts the quality of life for many individuals. This article explores the nature of this link, examining the underlying mechanisms and available strategies for diagnosis and management.
Confirming the Association with MS
Dry eyes are a common non-visual symptom experienced by people with MS, often overshadowed by symptoms like optic neuritis or double vision. Studies show that a substantial portion of the MS population experiences dry eye disease. Research indicates that up to 35% of patients show abnormal results on tear volume tests, suggesting a high frequency compared to the general population. Objective tests in one study revealed that more than 66% of MS patients had tear moisture levels significantly below the normal threshold, indicating a prevalent issue with tear production.
Ocular surface dryness often presents as a primary consequence of the MS disease process, but it can also be linked to co-occurring autoimmune disorders. Sjögren’s Syndrome, for example, is an autoimmune condition that specifically targets moisture-producing glands, including the lacrimal glands. Since both are autoimmune diseases, they can sometimes co-exist. This presents a diagnostic challenge where dry eye symptoms might be attributed to a secondary condition rather than MS alone.
While the overlap with Sjögren’s Syndrome does not appear significantly higher than in the general population, dry eye symptoms in the MS population remain a recognized clinical issue. Dry eye symptoms are often more severe in patients with higher levels of disability, suggesting a correlation between disease progression and ocular surface health issues. Recognizing dry eye as a legitimate symptom of MS, regardless of the direct cause, is an important step toward improving patient care and comfort.
Understanding the Mechanisms of Damage
The development of dry eyes in MS patients is usually a result of complex neurological damage, compounded by treatment side effects, rather than a single factor. One primary pathway involves damage to the body’s involuntary nervous system, known as autonomic dysfunction. Tear production is largely regulated by the parasympathetic branch of this system, which sends signals through the Facial Nerve (Cranial Nerve VII) to the lacrimal glands.
MS lesions in the brainstem or other central nervous system areas can interrupt these parasympathetic nerve signals before they reach the lacrimal gland. This disruption prevents the gland from receiving the command to secrete the aqueous, or watery, component of tears. This leads to aqueous-deficient dry eye. The key neurotransmitter in this process is acetylcholine, which acts on muscarinic receptors on the lacrimal gland cells to trigger tear release.
A second mechanism involves the Trigeminal Nerve (Cranial Nerve V), which is responsible for corneal sensation. Feedback from corneal sensory nerves stimulates the reflex arc for tear production and blinking. Damage to the Trigeminal Nerve pathway reduces corneal sensitivity, meaning the eye does not register dryness and fails to signal the lacrimal gland to produce tears.
Trigeminal Nerve damage can also affect motor control, leading to a reduced or incomplete blinking rate. This prevents the tear film from being evenly distributed across the ocular surface. This poor distribution causes existing tears to evaporate too quickly, contributing to evaporative dry eye disease. The lack of protective sensation also makes the cornea more vulnerable to damage from exposure.
A third contributing factor is the effect of medications used to manage MS symptoms and progression. Many symptomatic treatments, such as anticholinergic drugs prescribed for bladder dysfunction, can exacerbate dryness. These medications block the muscarinic acetylcholine receptors needed for tear production, directly suppressing the lacrimal gland’s function. Certain antidepressants, particularly tricyclic antidepressants used for pain management, also possess anticholinergic properties that can worsen dry eye symptoms.
Diagnosis and Management Options
The diagnosis of dry eye disease in a person with MS requires specific testing by an ophthalmologist to determine the type and severity of the condition. A common diagnostic procedure is the Schirmer’s test. This measures the volume of tears produced by placing small filter paper strips inside the lower eyelid for five minutes. Results below a certain threshold indicate aqueous-deficient dry eye.
Another standard test is the Tear Break-Up Time (TBUT). This measures how quickly the tear film evaporates from the eye surface after a blink, often using a dye like fluorescein. A rapid break-up time points toward an unstable tear film, characteristic of evaporative dry eye. Corneal staining with specialized dyes is also used to identify surface damage caused by chronic dryness.
Management begins with over-the-counter solutions, primarily artificial tears, designed to supplement the natural tear film. Preservative-free artificial tears are often recommended for frequent use because preservatives in standard drops can irritate an already compromised ocular surface. Gels and ointments are also available, providing a thicker, longer-lasting layer of lubrication, often best applied at night.
When over-the-counter options are insufficient, prescription medications can be used to address the underlying inflammation accompanying chronic dry eye. Topical drops containing immunomodulators, such as cyclosporine or lifitegrast, work by reducing inflammation in the lacrimal glands and on the eye surface. This helps restore the eye’s natural ability to produce tears.
For patients whose tears drain too quickly, a minor procedure can insert tiny silicone plugs, known as punctal plugs, into the tear drainage ducts. These plugs temporarily or permanently block drainage, retaining existing tears on the eye surface for longer periods. Lifestyle adjustments also play an important role in managing symptoms, such as using a humidifier, avoiding direct airflow from fans or heating vents, and wearing wraparound glasses outdoors to protect against wind.